BS EN ISO 8985:1998 download free.Plastics Ethylene/vinyl acetate copolymer (EVAC) thermoplastics Determination of vinyl acetate content.
BS EN ISO 8985 specifies two categories of method for the determination of the viny) acetate VAC) content of ethyleneivinyl acetate (EVAC) copolymers. for use in the designation of such copolymers in accordance with ISO 4613.1:1997. One category is referred to as “reference methods”, the other as “Lest methods”, NOTE The abbreviation previoualv used for ethylene/vinyl acetate copolvm’r (E/VAC) haa been replaced by the abbreviation EVAC (see ISO 1043-11997, Plastics — Symbols and cibbrcriuted terms — Part 1: Bwk polymers and their special characteristics)
The “reference methods” are used to calibrate the method used for the determination of the vinyl acetate content of ethylene/vinyl acetate copolymers.
The “test methods” are other methods which can be used for the determination if they are calibrated using one of the reference methods described in clause 3 provided they show a certain permissible repeatability.
2 Normative references
The following standards contain provisions which, through reference in this text, constitute provisions of BS EN ISO 8985. At the time of publication. the editions indicated were valid. All standards are subject to revision, and parties to agreements based on BS EN ISO 8985 are encouraged to investigate the possibility of applying the most recent editions of the standards indicated below. Members of IEC and ISO maintain registers of currently valid International Standards.
ISO 4613.1:1993, Plastics — Ethylene/vinyl acetate (EIVAQ moulding and extrusürn materials — Part 1: Designation and specification.
ISO 4799:1978. Laboratory glassware — (‘ondensers.
3 Reference methods
3.1 Reference method 1: Hydrolysis and back titration
3.1.1 Principle
A test portion is dissolved in xylene and the acetate groups are hydrolysed with alcoholic potassium hydroxide solution. An excess of sulfuric or hydrochloric acid is added. The acid is back titrated with a standard sodium hydroxide solution in the presence of phenophthalein as indicator.
3.1.2 Reagents
During the analysis. use only reagents of recognized analytical quality and distilled water or water of
equivalent purity.
3.1.2.1 Xykne.
3.1.2.2 Sulfuric acid, approx. 5 gIl solution, or hydrochoric acid. approx. 3,7 WI solution.
When analysing an unknown sample. first carry out a preliminary test under conditions which are valid for a copolymer containing 20 % to 40 % VAC.
3.1.4.1.2 Add 50 ml of xylene (3.1.2.1) to the contents of the flask and 25 ml of potassium hydroxide (3.1.2.3), using the pipette (3.1.3.3). Heat the flask, topped with the reflux condenser (3.1.3.7), for 2 hours using the heating apparatus. After hydrolysis, remove the flask from the heating apparatus and allow to cool to ambient temperature. Add 30 ml of sulfuric or hydrochloric acid (3.1.2.2). using the pipette (3.1.3.2), stopper the flask and shake vigorously. Add several drops of phenolphthalein solution (3.1.2.5) and titrate the excess acid with standard sodium hydroxide solution (3.1.2.4), shaking the flask (luring the titration.
3.1.4.2 Blank test
Carry out a blank test in parallel with the determination, following the same procedure and using the same reagents but omitting the test portion.
3.1.5 Expression of results
3.1.5.1 The vinyl acetate content w(VAC), expressed as a percentage by mass, is given by the formula:
w(VAC). 8.9(v- v2)c1
where
is the volume, in millilitres. of sodium hydroxide solution used for the determination:
v2 is the volume, in millilitres. of sodium hydroxide solution used for the blank test;
is the actual concentration, expressed in moles per litre, of the sodium hydroxide solution used for the titration:
m is the mass, in grams, of the test portion (see 3.1.4.1.1).
3.1.5.2 Carry out two determinations. If the results differ by more than 1 %, discard them and run the determinations again. Report the arithmetic mean of the two determinations.
3.1.6 Test report
The test report shall contain the following information:
a) a reference to BS EN ISO 8985 and the method used:
b) all details necessary for the complete identification of the sample;
c) the result. expressed in accordance with 3.1.5.2.
3.2.4.1.2 Add 25 ml of xylene (3.2.2.1) to the contents of the flask and 10 ml of hexan.1-ol (3.2.2.2) and 5 ml of potassium hydroxide solution (3.2.2.3). Heat the flask, topped with the reflux condenser (3.2.3.6). for 30 mm., using the heating apparatus (3.2.2.7) set at boiling temperature. After 30 mm., remove the flask from the heating apparatus and allow to cool for 5-6 mm., then introduce 35 ml of acetone (3.2.2.4) through the top of the condenser. Remove the condenser and place the flask (if conical) on the magnetic stirrer (3.2.2.9). otherwise transfer the solution to a beaker first. Immerse the glass electrode (sec 3.2.3.1) and one of the ends of the connecting bridge into the flask or beaker. Immerse the other end of the connecting bridge and the silver/silver chloride reference electrode (see 3.2.3.1) in the beaker filled with the ethanolic solution of lithium chloride (3.2.2.6).
Carry out the potentiometric titration immediately, adding standard hydrochloric acid (3.2.2.5) until the first drop in potential and stirring all the time. When close to the end point, add acid in 0,04 ml to 0,06 ml increnwnts.
When the end point is reached. read off the voltage, in millivolts, on the titrator as well as the volume of hydrochloric acid added.
The end point of the titration is that point at which the greatest variation in potential occurs for a given increment of acid added. In the event of two such points occurring, take the first value as the end point. The end point may also be determined graphically.
3.2.4.2 Blank test
Carry out a blank test in parallel with the determination, following the same procedure and using the same reagents but omitting the test portion. Plot the titration curve. The mean value of the peak on the titration curve is taken as the end point.
3.2.5 Expression of results
3.2.5.1 The vinyl acetate content w(VAC), expressed as a percentage by mass, is given by the formula:
w(VAC) = L609(v— V4)C2
where
v3 is the volume, in millilitres, of standard hydrochloric acid used for the blank test;
V4 is the volume; in millilitres, of standard hydrochloric acid solution used for the determination;
c2 is the actual concentration, in moles per litre, of the standard hydrochloric acid solution used for the titration;
m is the mass, in grams, of the test portion (see 3.2.4.1.1).
4.1.1 Principle
The vinyl acetate content is determined using infrared spectrometry. This method involves determining the ratio of the absorbance in the n(CH,) band at 2 678 cm and the 2n(CO) band at 34W) cm of an EVAC film with a thickness of between 50 im and 300 RIm. The absorbance ratio is converted to vinyl acetate content using a calibration curve established using standard EVAC reference specimens with known vinyl acetate contents measured as in clause 3. It is not necessary to know the exact thickness of the film as an infrared band is used as an internal reference.
NOTE 1 This method is suitable for samples containIng 10 “ (mlm) or more of VAC.
NOTE 2 The internal reference peak at 3 605 cm may be used as the internal rekrenct’ instead of the peak at 2 675 cm for samples with a thickness greater than 200 pm. If manual measurement of thickness is possible, it may be used instead of the absorbance at the internal reference peak.
NoTE 3 i drawback to this method is the possible interference by stahilisers or additives. Other CO peaks exist
at 610 cm. 1 020 cm1, 1 250 cm and 1 743 cm, however, and they can be used instead of the peak at 3460 cm, with a sample thickness appropriate to the VAC content of the sample.
4.1.2 Apparatus and materials
Standard laboratory equipment, plus the following:
4.1.2.1 Spectrometer, wave number range 4 000 cm to 600 cm1, capable of resolution to I cm.
4.1.2.2 Specimen holder.
4.1.2.3 Beam shutter.
4.1.2.4 Hot-pressing machine. supplying at least 10 MPa pressure, with hotplates which can achieve a temperature of 150 °C.
4.1.2.5 EVAC reference specimens, the vinyl acetate contents of which have been determined using one of the reference methods described in clause 3.
4.1.3 Procedure
4.1.3.1 Preparation of films
Prepare films of constant thickness using the hot-pressing machine (4.1.2.4) at approx. 150 °C. For VAC contents of less than or equal to 10 %, use 200 im to 300 1m. For VAC contents greater than 10 % use 50 lm to 150 im.
NOTE To assist with shaping and to prevent EVAC sticking to the plate surface, a thin film of polytetrafluoroethylene (I’TFE) may be used. Where the VAC content is less than 20%, the PTFE film may be replaced by aluminium foil.
4.1.3.2 Measurement
4.1.3.2.1 Calibrate the abscissa (wave number) and adjust the absorbance zero for 100% transmission through the spectrometer (4.1.2.1).
4.1.3.2.2 Insert an EVAC reference specimen (4.1.2.5) prepared in accordance with 4.1.3.1 into the.